As a result of both the increasing demand from consumers for additional ‘smart’ functionality in spray devices, and the ever-growing pressure to eliminate the greenhouse gas propellants inherent to traditional aerosol can technology, alternatives to traditional spray technologies are being sought. This has led to the rapid growth in the field of electronic spray technology, and a number of different spray generators have been proposed (U.S. Pat. No. 5,518,179 for example). Because the spray is electronically generated propellants are not required bringing environmental benefits. Additional benefits include controllable performance and an aesthetically pleasing droplet plume.
One area in which such technologies could play an important role is in consumer goods such as personal and household care products. For such products, and often for other spray devices, a degree of portability is a requirement. As such, there is a limit to the size the liquid reservoir can be. Most products in these areas are therefore designed to be fully disposable. Examples include perfume bottles, spray insecticides and detergent sprays. Generally, two technologies are conventionally employed to generate the spray using a conventional spray nozzle; manually operated pumps and pressurised reservoirs. For manually operated pumps, the flow rate is a function of how the consumer uses the device. For pressurised reservoir devices, flow rate is linked to reservoir pressure and is therefore very well controlled; consumers expect the same flow rate every time they use the device and the same flow rate from a new device when their current device runs out. For an electronic spray device, with the user just pressing a button to initiate spraying, a level of repeatability similar to current pressurised devices will be expected.
Electronic spray technologies by definition require a power source and electronic circuitry (henceforth referred to as a spray controller, see FIG. 1) to be incorporated or linked to the spray generator. Such components can add to the overall bill of materials cost. Coupling this to an increased awareness of the impact of waste on the environment leads to a strong requirement to ensure the power source and controller are used for an extended period of time and are not part of any disposable portion of the product. To meet this requirement at the same time as keeping liquid reservoir size reasonable has led to the use of a master and cartridge model in which high cost reusable components are contained in a master part of the overall device and the liquid is contained in a cartridge part of the overall device. When the liquid is used up the cartridge is replaced.
A further benefit of such a model is that it could allow a master component to interact with different cartridges either simultaneously or at different times. For example, a single master could be used to control several cartridges delivering different products (for example different paint types or colours, different fragrances, different skin care formulations). These cartridges could all be connected to the master at the same time or the consumer could connect the cartridge they wish to use to the master as and when they want to use it.
For all such devices, it is often beneficial to ensure all liquid contacting components including the spray generator are part of the cartridge. This avoids the need for a fluidic interface between the master and cartridge which can be complicated to implement in a low cost user friendly embodiment, increases the risk of leakage, requires the spray generator to have a long life and leads to cross-contamination if there is a wish to spray different liquids. Other device models to which the invention described here can also be applied are possible. This includes the spray generator being independently replaceable from both the master unit and the liquid containing cartridge.
For such a model to work, the master component needs to “know” what the product to be delivered is and how to deliver it. U.S. Pat. No. 6,712,287 discusses this requirement and various means for communicating the product type to the master. With such communication means in place, additional information can be exchanged and/or it can be used to inform the user of the product type. WO 2008/004194 includes an embodiment covering this in which information from or about the cartridge is displayed by the master.
This invention is associated with electronic sprays generators in which vibration is used to drive spray creation, more specifically in which vibration of a perforate membrane is used to drive spray creation. An exemplary embodiment of such a device can be found in the eFlow device sold by Pari GmbH. For such devices, the vibration is often generated by applying an alternating voltage across a unimorph or bimorph piezoceramic component or similar. The alternating voltage drives this component into oscillatory deformation at the drive frequency. This deformation is coupled to the perforate membrane causing it to vibrate and generate the liquid spray. Thus the characteristics of the input electrical waveform have a direct bearing on the spray that is generated. Similar drive mechanisms are often used for other electronic spray technologies to which this invention is also applicable.
Such spray generators often have a resonant frequency at which energy is efficiently transferred to the perforate membrane and hence to the liquid. To obtain good performance it is known that the spray generator must be operated at or at least close to the resonant frequency (EP 1,731,228 for example). This is generally achieved by the spray controller scanning a pre-programmed frequency band before commencing spraying and using the results of this to lock into the resonant frequency of the spray generator. The resonant frequency can be periodically checked by the controller whilst spraying so as to capture any shifts in resonant frequency due to changes in liquid loading for example. Such an approach can also be used to detect if a cartridge is present and/or if any liquid is in contact with the spray generator as this can significantly alter the resonant frequency. This information can be communicated to the user through the use of light and sound as is done on the eFlow system.
The resonant frequency of the device can be obtained in several ways. Whilst the various ways may give slightly differing results, all can be used when locking onto the frequency for operation. In an approach, the resonant frequency is characterised in that the power consumption at said frequency when driven with a fixed voltage signal, is greater than the power consumption of the device when driven at frequencies higher of lower than this frequency. In another approach, the resonant frequency is characterised in that the impedance at said frequency when driven with a fixed voltage signal, is lower than the impedance of the device when driven at frequencies higher of lower than this frequency. In another approach, the resonant frequency is characterised as the frequency at which the rate of change of phase with frequency is higher than the rate of change of phase with frequency of the device when driven at frequencies higher of lower than this frequency. All these approaches make use of the fundamental electrical characteristics of the spray generator; the impedance and phase of the device as a function of frequency at the time of spray delivery. EP1731228 WO2008114044 and WO2005097348 all describe such lock in methods.
Whilst scanning a frequency range and locking on to the resonant frequency can assist in the delivery of a more repeatable spray, it does not by itself deliver reliable and repeatable performance. In particular, it does not fully account for manufacturing variation and the impact such variation has on spray performance. For example, it does not account for the absolute impedance of the device which determines how much energy is delivered to it, nor does it account for the amount of this energy that is transferred to the liquid to drive the droplet generation process. This is in part because piezoceramic component performance can vary part to part and batch to batch. Combining this with build tolerances can lead to unacceptable variation in spray performance between spray generators, nominally of the same design. This is especially true for consumer devices in which costs must be kept low, the spray plume is visible to the user and flow rate rather than total dose is the critical performance parameter.